//九九乘法表
for (let i=1;i<10;i++) {
    let str=''
    for (let j=1;j<=i;j++) {
        str += j + "*" + i + "=" + i*j + '\t';
    }
    console.log(str);
}

//排序
let arr=[9,7,1,2,3,1,8,15,20,31]
let arr1=[]
for (let i of arr) {
    arr1[i]='2'
}
let arr2=[]
for (let j=0;j<=arr1.length;j++) {
    if (arr1[j] == '2') {
        arr2.push(j)
    }
}
console.log(arr2);
